Sexual risk compensation - increased risk behavior due to decreased perceived risk following introduction of a partially efficacious biomedical HIV prevention intervention - can offset both the individual (prevention of HIV acquisition) and public health (prevention of continuing transmission) benefits of these new prevention technologies. With the recently initiated and imminent roll-out of three such partially efficacious strategies (medical male circumcision, microbicides, and oral pre-exposure prophylaxis), understanding sexual risk compensation is critical in the U.S. and other countries hard hit by HIV. Yet, this is an understudied field, especially outside of the artificial context of large clinical trials in which participants receive intensive, repeated HIV prevention messages and the efficacy of the intervention is unknown. The recent roll-out in South Africa of medical male circumcision, the only widely available (yet partially protective) biomedical HIV prevention strategy, affords us a unique opportunity to examine sexual risk compensation in a real-world situation. Thus, we propose to study sexual risk compensation in public sector medical male circumcision facilities in KwaZulu- Natal, South Africa, to understand behavioral responses to partially protective biomedical interventions. We are seeking an R21 developmental grant, in response to RFA-MH-11-090, with the following Specific Aims: (1) Develop and determine the feasibility of procedures for the future R01 application relating to recruitment, retention, and data collection (including potential use of cell phones for interviews) in a cohort of newly- circumcised sexually active young men and a comparison group of men who screen as eligible for MMC but who do not get circumcised~ (2) Refine the assessment of sexual behavior to be able to collect data relevant to the timing and duration of sexual risk compensation, including event-level information about sexual encounters~ (3) Develop theory-driven measures of hypothesized determinants of sexual risk compensation, including perceptions and interpretations of partial efficacy to be used for theory testing in the future R01~ (4) Pilot these and other measures in a four-month cohort study of 90 sexually active men who undergo MMC and a comparison group of 30 uncircumcised men and obtain key statistical parameters (attrition rates, standard deviation/prevalence of key predictors, and outcomes) necessary to support estimates of sample size for a future R01 study~ and (5) Explore the perspectives of female sexual partners of circumcised men on partial efficacy of MMC and the context of risk negotiation that it presents.